Because of the use of various solvents in processes for treating particulate materials, and particularly granular materials, extraction apparatuses are used to separate an oil or solvent from the granular materials. This is accomplished in various ways. In one type of apparatus, granular materials are subjected to a bath, and the bath draws oil from the grains to form a miscella. The miscella can then be separated from the granular materials by a screen or other means. In any case, a large fraction of the solvent and miscella is extracted and transferred to a location away from the granular materials. In the type of process described, the grains might go through a number of baths and would eventually be dried prior to being transferred for further processing, storage, or shipment.
In another type of process, an apparatus having vertically stacked plenums in which the granular materials are disposed is employed. Each stage has a porous floor through which a fluid is passed to contact a bed of the grain disposed on the floor of the plenum. In such operations, a typical depth of granular material is 24 inches. It will be understood, however, that the depth of granular material may, in fact, range anywhere between 16 inches and 48 inches.
In this type of process each floor can be defined by generally parallel, upper and lower plates. A chamber can, thereby, be defined between the plates, heated air or steam, typically, being introduced into the chamber to heat the plates and, indirectly, the granular material while it is disposed on the floor of the plenum. The floor, however, employs staybolts which function to maintain the distance between the upper and lower plates. Further, the staybolts define conduits passing upwardly through a floor from one plenum into the next. A staybolt defines a conduit which passes through the chamber between the upper and lower plates, and the conduit is isolated from the chamber. Heated fluid (i.e., air or steam) can be injected into the lowest plenum to rise from plenum to plenum and pass through and treat the granular materials in each plenum as it passes therethrough.
In the prior art, the staybolts are affixed to the upper and lower plates in various ways. Typically, the length of a staybolt extends through the full dimension between the upper surface of the upper plate and the lower surface of the lower plate. In such a construction, heavy welds are employed (that is, the weld volume is significant). This not only results in a greater cost in manufacturing, but it can also result in shrinkage and distortion of the plates, as well as the possibility of leakage upwardly through a defective weld joint. Because welding is necessary at a location which can result in buildup of the weld material upwardly from the upper surface of the upper plate, expensive grinding can be necessary to make the upper surface of the upper plate substantially planar.
Various other attempts have been made to improve the manner in which staybolts are mounted. For example, an aperture formed in the upper plate has been made considerably smaller than the coaxial aperture in the lower plate. The staybolt is given a smaller axial dimension so that the upper axial end of the staybolt abuts a lower surface of the upper plate at a location radially outward from the periphery of the aperture in the upper plate. This attempted solution, however, can also presents problems. In this solution, there can be, and frequently is, difficulty in accessing the upper weld. If the staybolt is of a sufficient diameter to afford good access to the weld, then the staybolt is of such a large diameter that several apertures or holes must be provided in the top plate so as to enable a desired rate of fluid flow. In prior art structures employing this solution, the result has been the provision of a cluster of holes at each staybolt with relatively wide spacing of the staybolts in their respective clusters. In consequence, the pattern of gas flow contacting and treating the granular material above the tray is significantly non-uniform. This results in lower efficiency of operation of the apparatus.
It has been found that a phenomenon which typically results where there is proper and efficient functioning of a desolventizer apparatus is the generation of a roughly spherical-shaped fluid void in the particulate material disposed on the upper surface of the upper plate in the immediate proximity of an aperture through which processing fluid escapes upwardly. Similar sized and shaped voids are typically created above each aperture. Each void, where the depth of the granular or particulate material is approximately 24 inches, typically has a real dimension radius of between 3/4 and 1 inch. Such a void is created by the pressure and upward velocity of the processing fluid as it escapes through an upper egress port of a staybolt and into the surrounding particulate material. It is important, however, that adjacent apertures through which the processing fluid passes be on centers of at least two times the 3/4 to 1 inch radius dimension so that fluid voids generated above adjacent apertures do not interfere and thereby decrease the efficiency of the processing.
Furthermore, it has been found that the pattern of apertures passing through the chamber via staybolts should be substantially uniform across the top surface of the tray. It has been discovered that, if the apertures are clustered, processing fluid escaping upwardly through a cluster of apertures is more likely to combine and form a large diameter channel centered on the cluster of apertures. Such a phenomenon enables the fluid to escape from the bed without substantial contact with the particulate material.
A further drawback of this phenomenon is that the large diameter channel of escaping fluid will tend to define a geyser effect, and granular material will be spewed into the space above the bed of material. The geyser may rise to a sufficient height to entrain particulate material in the flow of fluid as it is drawn from the machine into a final vent system. When this occurs, the granular material may contaminate the vent system and cause problems in operation.
It is to these problems of the prior art and desirable features that the present invention is directed. It is an improved tray construction which accomplishes many of the mandates and solves many of the problems of the prior art.